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23 month, then such small amounts of transport should be made available, either to Civil Affairs or to UNRRA. We suspect that such matters are overlooked or postponed just because they are so small, and that a man thinking in terms of shells for an army is not likely to see the relative- importance of a package of insulin. Moreover, the objectives of Civil Affairs and UNRRA are not identical. The primary aim of Civil Affairs is to prevent civilian problems from hampering the armies : the primary aim of UNRRA is to provide relief. Now that the armies are handing over to the French Government complete control of the zone intérieure of France, it should be possible for UNRRA to begin its own work of relief even on a small scale. But it must be given the small but essential transport facilities required. PREGNANCY TESTS THERE are now three tests for pregnancy which depend on the demonstration of an increased quantity of chori- onic gonadotrophin in the urine. It is hard to know what names to use for them. Reference to the animal employed may lead to confusion-the " mouse " test , sounds all right, but the " rabbit " test is often mis- heard as- the " rapid " test, and as- for the third, the animal is strictly speaking neither frog nor toad, and " xenopus" sounds rather pompous. The use of epqnyms is the commoner practice, though the names Aschheim, Friedman, and Hogben are frequently mis- spelt. The Aschheim-Zondek test has already proved its reliability, and for many years Professor Crew was able to report a very low percentage of error with it from the Edinburgh Pregnancy Diagnosis Station. Almost every step in the procedure, from the preliminary weighing of the mice to the diurnal injections, the gassing, and the dissection and mounting of the ovaries, can be left to the trained technician, and only the inspection and reading of the ovaries need be undertaken by the director of the station. A big colony of mice, or a reliable supplier, is essential. By using 5 mice for each test, the occasional refractory animal is virtually eliminated, and false positives should be rare provided the weight, and therefore the age, of the mice has been carefully checked. The great disadvantage of this test is that it takes 5 days to perform. The Friedman test, which is now almost as well known, is perhaps more suited to the smaller laboratory than to the pregnancy diagnosis station. Small numbers of doe rabbits need to be kept in stock and each strictly segre- gated not only from bucks but from other does. The intravenous injection of the untreated, or simply filtered, urine demands some technical skill which is acquired by practice. Results may be read in 48 hours. The test animal can be eliminated as a possible source of error. A preliminary laparotomy will allow inspection of the ovaries before the test is begun ; 48 hours after injection of the urine for diagnosis another laparotomy may reveal the characteristic corpora lutea and hæmorrhagica of a positive test, or it may reveal no change in the appear- ance of the ovaries. Injection of a known urine of pregnancy will now make sure that the-individual rabbit will respond to chorionic gonadotrophin, and that the appearances found after the second laparotomy were those of a true negative test. This procedure, while bestowing on the test a high degree of accuracy, renders it unsuitable for use on a large scale. The Hogben test has the great advantage of speed, and only those familiar with pregnancy diagnosis tests will appreciate how important that is. A woman, . content to have missed her period by many days, will suddenly decide that she must know at once whether she is pregnant or not. Xenopus will give her the answer within a day. For some years difficulty was experienced in this country with the Hogben test because it was impossible to breed the animals. This difficulty has now been overcome. There is nevertheless one serious disadvantage to the test-if untreated urine or alcohol-precipitated extract is injected, it kills 15% or more of the animals. Preparation of the urine to make it less lethal is an elaborate process depending on the adsorption of the gonadotrophin on kaolin, but in a pregnancy diagnosis station this can of course be carried out on a a large scale without seriously inconveniencing the organisation. It is advisable to kill animals not showing extrusion of ova overnight, for in some cases ova are found in the oviducts on post-mortem examina- tion and an apparently negative test may prover to be positive. ’ From each of’ these three standard tests an accuracy of about 98-5% may be obtained provided a detailed technique is developed in the hands of experienced workers. The Friedman test is suited to the small laboratory with a qualified research-worker who will conduct most of the steps of the tests himself. The Aschheim-Zondek and Hogben tests are more suited to the pregnancy diagnosis station, where such manipula- tions as multiple- injections of animals and chemical preparation of the urine can be placed in the hands of trained technicians, the reading of results being alone left to a qualified director. Under such conditions minor variations in technique assume less importance. NUCLEAR TISSUE THE basis of practically all histology is the use of stains which distinguish the nucleus from the cytoplasm. By this device the minute structure of the whole body has been made out, and the sequence of changes which the nucleus undergoes in cell division has been observed. These are matters of common knowledge to most of us, however long ago we may have taken our final MB, but within the last 25 years the irrepressible biochemists have greatly disturbed this quiet little medical back- water. Their achievements, recently reviewed by Davidson and Waymouth,1 now constitute an important development in medical science. The nucleotides are the basis of all nuclear structure and there are, broadly speaking, two kinds. Both con- tain a purine or pyrimidine base, a carbohydrate and a phosphoric acid group, but they differ in that in one the carbohydrate is desoxyribose and in the other ribose. This apparently minor structural change confers considerable functional differences on the nucleotides. Those containing desoxyribose condense into molecules with molecular weights of upwards of 1,000,000, and are characteristically found in the nuclei of cells. The others condense less readily and are found mostly in the nucleolus, the cytoplasm, in cells without visible nuclei, and in viruses. Nucleotides containing ribose and adenine act as co-enzymes in cell respiration, and it is interesting to recall that two of the B vitamins-ribo- flavin and nicotinic acid-also enter into the composition of these enzyme systems. Ribose nucleotides are broken down by an enzyme which has now been isolated and crystallised. This enzyme is heat-stable-i.e., it is not destroyed at 100 ° C-and it has been prepared and utilised to differ- entiate the two kinds of nuclear material in cells. Within the last 8 years a method of " staining " nuclear material has been introduced by Caspersson of Stock- holm. The purine and pyrimidine bases absorb ultra- violet light much more intensely than any other cell constituents, and by using this light and photographing the cells through quartz lenses the distribution of nuclear material and alterations in its concentration can be .followed. Both these techniques have contributed greatly to our recent knowledge, but there are other contributors, one of them being the ultracentrifuge. By this instrument macromolecular complexes can be 1. Davidson, J. N., Waymouth, C. Nutr. Abstr. Rev. 1944, 14, 1.
